Optical element, and method for producing same

ABSTRACT

An optical element includes a base having a curved depression formed in a front surface thereof and a formed layer arranged on the base. The formed layer includes a main part in the depression as viewed from a depth direction of the depression and an overhang on the front surface of the base while connecting to the main part. An opposite surface of the main part to a surface thereof on a side of an inner surface of the depression is formed like a concave curve that is concave in a same direction as the inner surface of the depression. A predetermined surface of the main part that is opposed to the inner surface of the depression is provided with an optical function part.

This is a continuation application of copending application Ser. No.14/418,962, having a § 371 date of Feb. 2, 2015, which is a nationalstage filing based on PCT International Application No.PCT/JP2013/066326, filed on Jun. 13, 2013. The copending applicationSer. No. 14/418,962 is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to an optical element and a method ofproducing the same.

BACKGROUND ART

As a conventional method of producing an optical element, there is aknown method in which a formed layer to be provided with an opticalfunction part such as a grating is formed in the depression of a base bypressing a forming mold against a resin material arranged in thedepression of the base and curing the resin material (for example, seePatent Literatures 1 to 5).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open PublicationNo. 2006-177994

Patent Literature 2: Japanese Patent Application Laid-Open PublicationNo. 2007-199540

Patent Literature 3: Japanese Patent Application Laid-Open PublicationNo. 2003-266450

Patent Literature 4: Japanese Patent Application Laid-Open PublicationNo. 2005-173597

Patent Literature 5: Japanese Unexamined Patent Application Publication(Translation of PCT Application) No. 2005-520213

SUMMARY OF INVENTION Technical Problem

In the optical element produced by the method as described above,however, the formed layer as a whole is in the depression of the base,and, in addition, stress caused by temperature changes during use orother reasons concentrates on the depression of the base, so that theformed layer may be separated from the base. Moreover, shrinkage orexpansion of the formed layer resulting from temperature changes duringuse or other reasons may deform the optical function part provided inthe formed layer.

The present invention therefore aims to provide an optical element and amethod of producing the same in which separation of the formed layer anddeformation of the optical function part can be prevented.

Solution to Problem

An optical element according to an aspect of the present inventionincludes a base having a curved depression formed in a front surfacethereof and a formed layer arranged on the base. The formed layerincludes a first portion in the depression as viewed from a depthdirection of the depression and a second portion on the front surface ofthe base while connecting to the first portion. An opposite surface ofthe first portion to a surface thereof on a side of an inner surface ofthe depression is formed like a concave curve that is concave in a samedirection as the inner surface of the depression. A predeterminedsurface of the first portion that is opposed to the inner surface of thedepression is provided with an optical function part.

In this optical element, the opposite surface of the first portion tothe surface thereof on the side of the inner surface of the depressionof the base is formed like a concave curve that is concave in the samedirection as the inner surface of the curved depression of the base, sothat the change in thickness of the formed layer in the first portion isgradual. This configuration can reduce the effect of shrinkage caused inthe first portion, for example, when the formed layer is cured. Evenwhen stress caused by temperature changes during use or other reasonsconcentrates on the depression of the base, the second portion on thefront surface of the base while connecting to the first portion pressesthe first portion in the depression of the base. Separation of theformed layer from the base is thereby prevented. In addition, shrinkageor expansion of the formed layer resulting from temperature changesduring use or other reasons is absorbed by the second portion on thefront surface of the base, so that shrinkage or expansion of the firstportion in the depression of the base is alleviated. Consequently,deformation of the predetermined surface of the first portion isprevented and deformation of the optical function part provided at thepredetermined surface is prevented accordingly. As described above, inthis optical element, separation of the formed layer and deformation ofthe optical function part can be prevented.

A groove portion may be provided outside of an opening of the depressionin the front surface of the base. The second portion may be embedded inthe groove portion. Spreading of the second portion of the formed layeron the front surface of the substrate thereby can be controlled. Sincethe second portion is embedded in the groove, the fixing strength of theformed layer to the base can be improved.

The curvature of the depression of the base may be greater than thecurvature of the concave curve of the opposite surface of the firstportion to the surface thereof on the side of the inner surface of thedepression. According to this configuration, for example, when theformed layer is formed by pressing a forming mold, the front end of theforming mold does not come into abutment with the inner surface of thedepression of the base, thereby suppressing damage to the inner surfaceof the depression of the base and to the forming mold.

The thickness of the second portion in the depth direction of thedepression may be greater than the thickness of the first portion in thedepth direction of the depression. This configuration can suppressdeformation of the first portion of the formed layer.

The optical function part may be a grating. Alternatively, the opticalfunction part may be a mirror. According to these configurations, agrating element or a mirror element with a simple construction can beobtained.

A method of producing an optical element according to an aspect of thepresent invention includes: a step of preparing a base having a curveddepression formed in a front surface thereof; a step of arranging aforming material on the base; and a step of pressing a forming moldagainst the forming material and curing the forming material therebyforming a formed layer having a first portion in the depression asviewed from a depth direction of the depression and a second portion onthe front surface of the base while connecting to the first portion. Anopposite surface of the first portion to a surface thereof on a side ofan inner surface of the depression is formed like a concave curve thatis concave in a same direction as the inner surface of the depression.The forming mold is provided with a forming surface for forming apredetermined surface to be provided with an optical function part inthe first portion such that the predetermined surface is opposed to theinner surface of the depression.

In this method of producing an optical element, the opposite surface ofthe first portion to the surface thereof on the side of the innersurface of the depression of the base is formed like a concave curvethat is concave in the same direction as the inner surface of the curveddepression of the base, so that the change in thickness of the formedlayer in the first portion is gradual. This configuration can reduce theeffect of shrinkage caused in the first portion, for example, when theformed layer is cured. Even when the forming material shrinks duringcuring, the second portion on the front surface of the base whileconnecting to the first portion shrinks in precedence to the firstportion, thereby alleviating shrinkage of the first portion in thedepression of the base. Consequently, deformation of the predeterminedsurface of the first portion is prevented and deformation of the opticalfunction part provided at the predetermined surface is preventedaccordingly. In addition, even when stress caused by temperature changesduring production or other reasons concentrates on the depression of thebase, the second portion on the front surface of the base presses thefirst portion in the depression of the base. Separation of the formedlayer from the base is thereby prevented. As described above, with thismethod of producing an optical element, separation of the formed layerand deformation of the optical function part can be prevented.

Advantageous Effects of Invention

According to an aspect of the present invention, separation of theformed layer and deformation of the optical function part can beprevented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an optical element according to an embodimentof the present invention.

FIG. 2 is an end view of the optical element taken along the line II-IIin FIG. 1.

FIG. 3 is a plan view of a substrate in a step of a method of producingthe optical element in FIG. 1.

FIG. 4 is a plan view of the substrate in a step subsequent to the stepin FIG. 3.

FIG. 5 is a cross-sectional view of the substrate taken along the lineV-V in FIG. 4.

FIG. 6 is a plan view of the substrate in a step subsequent to the stepin FIG. 4.

FIGS. 7(a) and (b) are cross-sectional views of the optical elementaccording to other embodiments of the present invention.

FIGS. 8(a) and (b) are views of the optical element according to otherembodiments of the present invention, where FIG. 8(a) is a plan view andFIG. 8(b) is an end view along line VIIIb-VIIIb in FIG. 8(a).

FIG. 9(a) to (c) are plan views showing examples of a groove in theoptical element according to other embodiments of the present invention.

FIG. 10 is an end plan view of the optical element according to yetanother embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described in detailsbelow with reference to the drawings. It is noted that in the drawingsthe same or corresponding parts are denoted with the same referencesigns and an overlapping description will be omitted.

As shown in FIG. 1 and FIG. 2, an optical element 1 includes an opticalfunction part 10 that is a reflective grating. The optical function part10 diffracts and reflects light L incident from one side. The opticalelement 1 includes a base 2 formed like a square plate (for example,outer shape of 8 mm×8 mm, thickness of 1 mm) made of silicon, plastic,ceramic, glass, or other substances. A depression 3 having a sphericalinner surface 3 b is formed in a front surface 2 a of the base 2. Thematerial of the base 2 is not limited to the materials described above,and the base 2 can be formed with a variety of materials by forming,cutting, etching, or other means. The inner surface 3 b of thedepression 3 may not have a spherical shape but may have a non-sphericalshape.

On the base 2, a formed layer 4 is arranged which is formed byphotocuring an optical resin for replicas, such as photocurable epoxyresins, acrylic resins, fluorocarbon resins, silicone, ororganic-inorganic hybrid resins. The formed layer 4 has a circular shapeas viewed from the depth direction (that is, one side) of the depression3. The material of the formed layer 4 is not limited to photocurableresins as described above and a variety of materials (forming materials)capable of forming with a forming mold 30 described later and curing canbe applied, such as thermosetting resin materials, low-melting glass, ororganic-inorganic hybrid glass.

The formed layer 4 includes a main part (first portion) 5 and anoverhang (second portion) 6 that are integrally formed. The main part 5is in the depression 3 as viewed from the depth direction of thedepression 3 and covers the inner surface 3 b of the depression 3 as awhole. The overhang 6 is on the front surface 2 a of the base 2, beingconnected to the main part 5, and is provided outside of an annularopening 3 a. That is, the overhang 6 is provided so as to surround thedepression 3. The thickness of the overhang 6 in the depth direction ofthe depression 3 is greater than the thickness of the main part 5 in thedepth direction of the depression 3.

In the formed layer 4, a curved surface 4 c formed like a concave curveis provided at a part of a surface 4 b (a predetermined surface)(hereinafter referred to as the “front surface” of the formed layer 4)on the side opposite to the side of the base 2 that corresponds to themain part 5. The curved surface 4 c is concave in the same direction asthe inner surface 3 b of the depression 3. That is, that part of theformed layer 4 which corresponds to the main part 5 is arranged alongthe inner surface 3 b of the depression 3 of the base 2. In the presentembodiment, the curvature of the curved surface 4 c of the main part 5is formed to be equal to the curvature of the inner surface 3 b of thedepression 3.

In a predetermined area of the curved surface 4 c on the main part 5, agrating pattern is formed which corresponds to a brazed grating having aserrated cross section, a binary grating having a rectangular crosssection, a holographic grating having a sinusoidal cross section, orother gratings.

On the front surface 4 b of the formed layer 4, a reflective film 7 thatis a deposited film of Al, Au, or other substances is formed. Thereflective film 7 is formed so as to correspond to the grating patternin the predetermined area of the front surface 4 b on the main part 5,and this part serves as the optical function part 10 that is areflective grating. The material of the reflective film 7 is not limitedto the materials described above and a variety of materials can beapplied. A protective film or an antireflection film of SiO2, SiN, MgF2,or other substances may be formed on the reflective film 7 bydeposition, sputtering, CVD, or other processes. A bonding layer of Cr,Ni, NiCr, Ti, TiN, or other substances may be formed between the formedlayer 4 and the reflective film 7 by deposition, sputtering, CVD, orother processes.

As described above, in the optical element 1, the curved surface 4 c,which is the part of the front surface 4 b of the formed layer 4 thatcorresponds to the main part 5, is formed like a concave curve that isconcave in the same direction as the inner surface 3 b of the depression3 of the base 2, so that the change in thickness of the formed layer 4in the main part 5 is gradual. In the present embodiment, in particular,the curvature of the curved surface 4 c of the main part 5 is formed tobe equal to the curvature of the inner surface 3 b of the depression 3,so that the thickness of the formed layer 4 in the main part 5 can bereduced (for example, 1 μm to 100 μm). This configuration can reduce theeffect of shrinkage caused, for example, when the formed layer is curedwith UV radiation or heat. In addition, even when stress caused bytemperature changes during use or other reasons concentrates on thedepression 3 of the base 2, the overhang 6 on the front surface 2 a ofthe base 2 and connected to the main part 5 presses the main part 5 inthe depression 3 of the base 2. This effect is attributable to that thefront surface 2 a with the overhang 6 thereon is a surface discontinuousfrom the inner surface 3 b of the depression 3 (in the optical element1, the curved, inner surface 3 b of the depression 3 is connected withthe planar, front surface 2 a). In addition, since the overhang 6 isprovided so as to surround the depression 3, the main part 5 is presseduniformly from the periphery. Separation of the formed layer 4 from thebase 2 is thereby reliably prevented.

Moreover, shrinkage or expansion of the formed layer 4 resulting fromtemperature changes during use or other reasons is absorbed by theoverhang 6 on the front surface 2 a of the base 2, so that shrinkage orexpansion of the main part 5 in the depression 3 of the base 2 isalleviated. In addition, since the overhang 6 is provided so as tosurround the depression 3, shrinkage or expansion of the main part 5 isuniformly alleviated. The thickness of the overhang 6 is formed to begreater than the thickness of the main part 5. Consequently, deformationof the curved surface 4 c of the main part 5 is reliably prevented anddeformation of the optical function part 10 provided at the curvedsurface 4 c is reliably prevented accordingly. In the optical element 1,therefore, separation of the formed layer 4 and deformation of theoptical function part 10 can be reliably prevented with a simpleconstruction.

Next, a method of producing the optical element 1 described above willbe described. First, as shown in FIG. 3, a substrate 20, for example,made of silicon is prepared. The substrate 20 is cut (diced) into a gridpattern, resulting in a plurality of bases 2. In the front surface 20 aof the substrate 20, the depression 3 is then formed for each of thefront surfaces 2 a of the bases 2 by etching or other processes. Aplurality of bases 2 each having the depression 3 in the front surface 2a are thus prepared. Subsequently, on the front surface 20 a of thesubstrate 20, a forming material (here, a photocurable resin material)for producing the formed layer 4 is arranged for each of the depressions3 of the bases 2. The forming material is thus arranged on a pluralityof bases 2.

Subsequently, as shown in FIG. 4 and FIG. 5, a forming mold 30 ispressed against the forming material for each of the depressions 3 ofthe bases 2. In this state, light (for example, ultraviolet rays) forphotocuring the forming material is transmitted through the forming mold30 and applied to the forming material to cure the forming material,thereby forming the formed layer 4 having the main part 5 and theoverhang 6. The formed layer 4 may be further thermally cured after theforming mold 30 is released from the formed layer 4. If the base 2 hastransparency to light for photocuring the forming material, the lightmay be transmitted through the base 2 and applied to the formingmaterial. The method of curing the forming material is not limited tophotocuring and a variety of curing methods such as thermal curing canbe applied depending on the kinds of the forming material. In the casewhere the formed layer 4 is thermally cured, the forming mold 30 is notlimited to the one having transparency and may be formed of a metal suchas nickel.

The forming mold 30 is provided with a forming surface 30 a for formingthe curved surface 4 c to be provided with the optical function part 10in the front surface 4 b of the formed layer 4. Here, the formingsurface 30 a is a convex curved surface complementary to the curvedsurface 4 c.

Subsequently, as shown in FIG. 6, the reflective film 7 is formed on thefront surface 4 b of the formed layer 4 by depositing Al, Au, or othersubstances, and the optical function part 10 is provided for each curvedsurface 4 c. The deposition is performed on the entire surface of thefront surface 4 b or any given range of the front surface 4 b (maskdeposition), as necessary. The substrate 20 is then cut (diced) into agrid pattern, resulting in a plurality of optical elements 1 as gratingelements. The forming of a plastic material, glass, or ceramic may beused to obtain the base 2 having the depression 3. The reflective film 7may be formed by sputtering or CVD, rather than deposition.

As described above, in the method of producing the optical element 1,the curved surface 4 c, which is the part of the front surface 4 b ofthe formed layer 4 that corresponds to the main part 5, is formed like aconcave curve that is concave in the same direction as the inner surface3 b of the depression 3 of the base 2, so that the change in thicknessof the formed layer 4 in the main part 5 is gradual. In particular, whenthe curvature of the curved surface 4 c of the main part 5 is set equalto the curvature of the inner surface 3 b of the depression 3, thethickness of the formed layer 4 in the main part 5 can be constant. Thisconfiguration can reduce the effect of shrinkage caused, for example,when the formed layer is cured by UV radiation or heat. In the method ofproducing the optical element 1, even when the forming material shrinksduring curing, the overhang 6 on the front surface 2 a of the base 2while connecting to the main part 5 shrinks in precedence to the mainpart 5, thereby alleviating shrinkage of the main part 5 in thedepression 3 of the base 2. In addition, since the overhang 6 isprovided so as to surround the depression 3, shrinkage of the main part5 is uniformly alleviated. Consequently, deformation of the curvedsurface 4 c of the main part 5 is reliably prevented and deformation ofthe optical function part 10 provided at the curved surface 4 c isreliably prevented accordingly.

In addition, even when stress caused by temperature changes duringproduction or other reasons concentrates on the depression 3 of the base2, the overhang 6 on the front surface 2 a of the base 2 presses themain part 5 in the depression 3 of the base 2. Moreover, since theoverhang 6 is provided so as to surround the depression 3, the main part5 is pressed uniformly from the periphery. Separation of the formedlayer 4 from the base 2 is thereby reliably prevented. With the methodof producing the optical element 1, therefore, separation of the formedlayer 4 and deformation of the optical function part 10 can be reliablyprevented.

The peripheral edge of the forming surface 30 a of the forming mold 30may be shaped so as to extend outward from the opening 3 a of thedepression 3. In this case, when the forming mold 30 is pressed againstthe forming material, the front end of the forming mold 30 is preventedfrom burying in the forming material and the forming material isprevented from coming around to the side surface 30 b of the formingmold 30. Accordingly, when the forming mold 30 is pressed against theforming material, the forming material comes into abutment only with theforming surface 30 a, thereby improving the releasability of the formingmold 30.

An embodiment of the present invention has been described above.However, the present invention is not limited to the foregoingembodiment. For example, as shown in FIG. 7(a), the curvature of theinner surface 3 b of the depression 3 of the base 2 can be set greaterthan the curvature of the forming surface 30 a of the forming mold 30.According to this manner, when the formed layer 4 is formed by pressingthe forming mold 30, the forming surface 30 a of the forming mold 30does not come into abutment with the inner surface 3 b of the depression3 of the base 2, thereby suppressing damage to the inner surface 3 b ofthe depression 3 of the base 2 and to the forming mold 30.Alternatively, as shown in FIG. 7(b), the curvature of the inner surface3 b of the depression 3 of the base 2 may be set smaller than thecurvature of the forming surface 30 a of the forming mold 30. The formedlayer 4 that is thin at the center of the main part 5 is thus obtained.The optical function part 10 is formed at the thin part of the main part5, whereby even when the formed layer 4 shrinks due to heat during useor other reasons, the ratio of shrinkage is small, because the thicknessis small at the part where the optical function part 10 is formed. Thisconfiguration can suppress the effect of shrinkage of the formed layer 4on the optical function part 10.

As shown in FIG. 8(a) and FIG. 8(b), in the front surface 2 a of thebase 2, a groove (groove portion) 8 may be provided outside of theopening 3 a of the depression 3. This groove 8 may be formed in anannular shape surrounding the depression 3. In this case, when theforming mold 30 is pressed against the forming material arranged on thebase 2, the forming material enters the groove 8. That is, when theforming material spreads outward from the depression 3, the formingmaterial enters the groove 8 thereby restraining the spreading of theforming material. The forming material is cured in this state, so thatthe overhang 6 is embedded in the groove 8. As described above, thespreading of the overhang 6 of the formed layer 4 on the front surface 2a of the base 2 can be controlled by providing the groove 8 in the frontsurface 2 a of the base 2. Accordingly, the base 2 can be reduced insize or the depression 3 can be increased in size. In addition, thefixing strength of the formed layer 4 to the base 2 can be improvedbecause the overhang 6 is embedded in the groove 8.

As a modification to the groove 8 provided in the front surface 2 a ofthe base 2, as shown in FIG. 9(a), in the front surface 2 a of the base2, linear grooves 8 a to 8 d may be provided so as to surround thedepression 3 at a position outside of the opening 3 a of the depression3. A predetermined gap is provided between theses grooves 8 a to 8 d.Alternatively, as shown in FIG. 9(b), in the front surface 2 a of thebase 2, a groove 8 e shaped like a square frame may be provided so as tosurround the depression 3 at a position outside of the opening 3 a ofthe depression 3. Alternatively, as shown in FIG. 9(c), in the frontsurface 2 a of the base 2, a pair of grooves 8 f, 8 g may be providedwith the depression 3 interposed therebetween at a position outside ofthe opening 3 a of the depression 3, and grooves 8 h, 8 i may beprovided to extend from the grooves 8 f, 8 g, respectively, to connectto the outer edge of the base 2. Also in those cases, the formingmaterial enters the groove, thereby controlling the spreading of theoverhang 6 of the formed layer 4 on the front surface 2 a of the base 2.

The optical function part 10 is not limited to a grating and may have avariety of optical functions. As an example, as shown in FIG. 10, theoptical function part 10 may be formed as a mirror, rather than forminga grating pattern on the curved surface 4 c of the formed layer 4 and onthe reflective film 7. In this case, a mirror element with a simpleconfiguration can be obtained. The refractive index may be matched atthe interface between the base 2 and the formed layer 4, and light L maybe applied to the optical function part 10 from the side of the base 2(the other side). When light L is applied from either one side or theother side, the reflective film 7 may not be provided and light L may betransmitted through the optical function part 10 (for example, atransparent grating).

The predetermined surface of the formed layer 4 that is provided withthe optical function part 10 is not limited to the curved surface 4 c.The predetermined may be a part of the front surface 4 b that extendsfrom the main part 5 to the overhang 6.

As shown, for example, in FIG. 1, the overhang 6 is formed in an annularshape so as to surround the depression 3. However, the overhung 6 maynot be annular and may be provided only on one side.

A depression may be provided in place of the groove 8 in the frontsurface 2 a of the base 2. A rectangular depression or a circulardepression may be employed as this depression. Also in this case, theoverhang 6 enters the depression provided in place of the groove 8,thereby improving the fixing strength of the formed layer 4. In the casewhere the base 2 is rectangular and the opening 3 a of the depression 3is circular as viewed from the depth direction of the depressionprovided in place of the groove 8, depressions (the depression providedin place of the groove 8) are provided with the depression 3 interposedtherebetween on a diagonal line of the base 2, so that the base 2 can bereduced in size or the area of the opening 3 a can be increased.

A plurality of optical elements 1 are obtained by cutting (dicing) thesubstrate 20 into a grid pattern. However, the optical elements 1 can beformed one by one.

INDUSTRIAL APPLICABILITY

According to an aspect of the present invention, an optical element anda method of producing the same are provided, in which separation of theformed layer and deformation of the optical function part can beprevented.

REFERENCE SIGNS LIST

1 optical element, 2 . . . base, 2 a . . . front surface, 3 . . .depression, 3 a . . . opening, 3 b . . . inner surface, 4 . . . formedlayer, 4 b . . . front surface (predetermined surface), 4 c . . . curvedsurface (opposite surface), 5 . . . main part (first portion), 6 . . .overhang (second portion), 8, 8 a to 8 i . . . groove (groove portion),10 . . . optical function part, 30 . . . forming mold, 30 a . . .forming surface.

The invention claimed is:
 1. An optical element comprising: a basehaving a depressed surface, the depressed surface having a periphery anda depth; a formed layer provided on the depressed surface of the baseand having a depressed surface, the formed layer including an area inwhich a grating groove is formed and an area in which the grating grooveis not formed, the area in which the grating groove is not formedsurrounding the area in which the grating groove is formed; and areflective film provided on the depressed surface of the formed layer,the formed layer comprises a different material than the reflectivefilm, at least part of the surface of the reflective film formed on thearea of the formed layer in which the grating groove is formed ispositioned in a position deeper than the periphery of the depressedsurface of the base, and the base comprises a material that is differentfrom that of the formed layer, wherein, in the area of the formed layerin which the grating groove is formed, the thickness from a bottomportion of the depressed surface of the base to a bottom portion of thebase is greater than the depth of the depressed surface of the base. 2.The optical element according to claim 1, wherein the grating grooveextends in a direction crossing the area of the formed layer in whichthe grating groove is formed.